1. Field of the Invention
The present invention relates to a method for protruding an armature shaft from the specified end face of a core specified dimension when pressing the armature shaft into an axial hole of an approximately cylindrical shaped core, which is one of the component members of the armature, and a pressing apparatus for the same.
2. Background Art
FIG. 5 shows a core 2 which is one of the component members of an armature which is a rotating portion for such a motor. The core 2 comprises a plurality of thin silicon steel plates (thickness: approximately 0.35 to 1.00 mm) laminated to form an approximately cylindrical shape and has a plurality of slot 2c formed around its peripheral surface. An axial hole into which an armature shaft 1 (hereafter referred to as the shaft 1) is pressed and mounted, is formed at a shaft center P of the core 2 and the openings of the axial hole are formed at upper and lower end faces of the core 2. Furthermore, a recess portion 2d is formed coaxially with the axial hole into a cubical shape at the desired depth at one end face 2b of the core 2.
The diameter of the shaft 1 is approximately equal to the bore of the axial hole and a plurality of grooves are formed in the axial direction on the peripheral surface of the shaft 1. Furthermore, because the length of the shaft 1 is longer than that of the core 2, both ends 1a and 1b of the shaft 1 protrude from the respective end faces of the core 2.
One end 1a of the shaft 1 protrudes out a distance from the opposite end face 2a of the core 2 not having the recess portion 2d at a dimensional tolerance X range of -0.1 mm&lt;X&lt;0 of the specified distance. Hereafter, the end face 2a will be referred to as a specified end face 2a. Because a connection body (not shown) for engaging with other rotating members (not shown) is molded on with resin at the end 1b of the shaft 1, protruding from the end face 2b into which the recess portion 2d is formed, a protrusion dimension of the shaft 1 from the end face 2b of the core 2, moreover, its dimensional tolerance are not specified in particular. Hereafter, the end face 2b will be referred to as the molded end face 2b.
The above-mentioned conventional method for pressing the shaft 1 into the axial hole of the core 2, is carried out by using a conventional pressing apparatus using operated by such means as hydraulic drive in the following way. The shaft 1 is inserted into the axial hole from the side of the molded end face 2b and a pressing portion of the pressing apparatus presses the shaft 1 into the axial hole while alternating repeated pressing and stopping motions and measuring the protrusion of the shaft 1 from the molded end face 2b until the specified protrusion dimension is reached. When the protrusion dimension of the shaft 1 from the molded end face 2b becomes equal to the specified dimension, a protrusion dimension of the shaft 1 from the specified end face 2a is deduced therefrom.
However, in the above-mentioned conventional method for press fitting the shaft, because the pressing and measuring motions are repeated alternately, the assembly operation is time consuming and inefficient and a mechanism and a controlling method of the pressing apparatus is complex. Furthermore, since the specified dimensional tolerance Y of the whole length of the shaft 1 pressed into the axial hole of the core 2 is in the range of -0.2 mm&lt;Y&lt;+0.2 mm, which is larger than the above-mentioned dimensional tolerance X concerning the protrusion of the shaft 1 from the specified face 2a, the use of the above-mentioned conventional pressing method make it difficult to confidently assume the protrusion dimension.